TV Segment on own video production

[Dota]

Hi, I was wondering about the legalities surrounding the usage of a segment of a television program on one's own commercial video. For instance, if one were to make an internet television program, would he/she be allowed to use video of a tv set which displays a particular television program? I usually see tv shows which have characters watching a television set, but rarely if ever do I see the show itself being displayed on the television set's screen (which the characters are watching)...is this due to usage restrictions?

 

[Michael Wechsler]

Why do you need to use footage from an actual television program and get yourself into potential trouble?